Non-aqueous electrolyte secondary batteries employing lithium compounds as anode materials have high voltages and high energy densities, and have therefore been actively studied. In particular, when interest in lithium as an anode material was developing, lithium metals with large capacities were studied. However, in lithium metal anodes, lithium dendrites grow on the lithium surface during charging. Therefore, charge/discharge efficiency decreases and short circuits between the anode and cathode may occur. Furthermore, lithium metal anodes are instable due to the high reactivity of lithium.
On the other hand, the expansion and contraction during charge/discharge cycles of anodes made of carbonaceous materials is less than that of anodes made of lithium or lithium alloys. However, carbonaceous anode materials have reduced capacity (about 350 mAh/g) and reduced initial charge/discharge efficiency relative to lithium anode materials. Thus, despite the disadvantages of metal anodes, attempts have been ongoing to enhance battery capacity of metal anodes such as lithium.
It is known that lithium metals and lithium alloys such as lithium-aluminum, lithium-lead, lithium-tin, and lithium-silicon can provide larger electric capacities (2,000 mAh/g or more) than carbonaceous materials. However, when lithium metals or lithium alloys are used alone, lithium dendrite formation and rapid volume change can occur. Thus, appropriate combinations of lithium metals or lithium alloys with carbonaceous materials as anode materials have been studied to increase electric capacity and prevent short circuits between the anode and cathode.
Various conventional techniques using such composite anode materials have been suggested. However, these techniques are based on coating metal particulate surfaces with carbon particles, etc. to prevent lithium dendrite formation, which occurs with metal materials, and to enhance charge/discharge capacities, which are lower with carbonaceous materials.
The carbonaceous materials used in these conventional techniques have low electric capacity and conductivity, thereby restricting the enhancements in initial charge/discharge efficiency and discharge capacity. Therefore, a more practical anode active material having good initial charge/discharge efficiency and high discharge capacity is needed.